Nucleosomes containing Sin mutant histones are more likely to dissociate during pol II transcription. (A) DNA-labelled nucleosomes containing wild-type or Sin mutant histones were transcribed by yeast pol II at the indicated KCl concentrations; intact complexes were then resolved from free DNA by native polyacrylamide gel electrophoresis. Only the region of the gel in which free DNA appears is shown; an example of the entire native gel from such an experiment is shown in supplementary Fig S4 online. No-chase control (nc): Transcription was performed in the absence of UTP and pol II was stalled upstream of the nucleosome. (B) The amounts of histone-free DNA produced after transcription at 150 mM KCl were quantified and normalized to the overall amount of active ECs. EC, elongation complex; H3, histone H3; H4, histone H4; pol II, polymerase II.